// Comments are added at several places to original function.

// This function partitions array elements to the left
// and right of pivot. It is used by quick sort function.
size_t partition(int * arr, int l, int r) 
{
	int i = l + 1, j = r;
	// Left item is selected as pivot.
	int pivot = arr[l];	
	
	while (i <= j) 
	{
		while (pivot < arr[j])
			j--;
		if (j == l)
			return l;
		while (i < r && pivot > arr[i])
			i++;
		if (i == j) break;
		// Swapped to strictly put items to the left and right of pivot.
		if (i < j)
			swap(&arr[i], &arr[j]);
	}
	swap(&arr[l], &arr[j]);	
	return j;
}